Pressure switches are often considered commodity items. But for many mission-critical or demanding applications, including high-pressure hydraulics, aerospace, pharmaceuticals and more, a switch may require a custom mechanical design or electrical features that go beyond what commercial off-the-shelf switches can offer. In fact, with a little extra engineering, users can boost a switch’s performance and, in many instances, overcome challenges a pressure system may be experiencing as a result of its operating environment.
Pressure switches from Sigma-Netics
Recent applications demonstrate how custom-engineering Sigma-Netics pressure switches has improved the functionality of the switch — as well as the reliability of the overall system. These additional features include incorporating signal delay, thermal lockout and dual-switch capabilities, as well as outfitting switches with a flush-mount design to better-fit tubular structures in processing machines.
If a hydraulic system suffers from pressure spikes, its pressure switches may not work as expected. The spikes can trigger the switch prematurely even though continuous pressures remain below the set point. The result is a hard-to-control hydraulic system plagued by false switching signals. Fortunately, a simple solution exists to prevent these spike-induced switching errors: just add a time delay to the switch.
A custom pressure switch with a time delay from Sigma-Netics eliminated false signals.
In an off-road vehicle, a pressure switch was used as part of a hydraulic monitoring system, which was designed to trigger a warning light in the cabin if it experienced sustained excess pressure. But driving over rough terrain was causing unintended pressure spikes, causing the annunciator light in the crew compartment to constantly switch on and off. Sigma-Netics engineers incorporated a PC board into the pressure switch that was programmed to delay signal output based on certain adjustable parameters, including the amount of time — down to the millisecond — and whether the signal occurred on the rising or falling pressure. In this case, engineers set the time delay at 3.2 seconds. As a result, the warning light remained off unless a pressure change lasted longer than that.
In addition to integrating time delay capabilities, the pressure switch used in the off-road vehicle had to be ruggedized for use in demanding environments. Sigma-Netics designs all of its pressure switches to withstand pressure spikes, leaks, temperature extremes, moisture, chemical exposure, vibration and shock loads.
Other ruggedized features of this custom design included:
- Proof pressures up to 12,000 psig
- Maximum operating pressures up to 7,500 psig
- Wide temperature range of -40 to 250°F
- High overpressure capability
- High shock and vibration survivability
- Snap-action electrical switch tested to 1 million cycles
- IP67 compliance
In aircraft hydraulic applications, cold start-ups often cause pressure-switching errors that disappear once the system reaches its normal operating temperature. The culprit behind these false high-pressure signals is increased fluid viscosity, which temporarily increases the differential pressure across the diaphragm or pressure-sensing device. A thermal lockout mechanism based on a snap-acting, temperature-sensitive bimetallic disc can prevent this problem.
A thermal lockout mechanism incorporated into an aircraft hydraulic system prevents false high-pressure signals.
Finally, some applications may benefit from using a single pressure switch with two distinct switching elements. This Double Pole Double Throw (DPDT) configuration saves on installation real estate and provides greater design flexibility. With this arrangement, one pressurized system can output to two different electrical circuits, increasing control options and doubling available amperage. Users can also integrate different circuits and contact material into the switching element, including gold contacts for low-level dry circuits, as well as silver contacts for circuits requiring higher amperages. For critical applications, this kind of design also provides redundancy in the event a switching element fails. And finally, this design saves space — allowing users to run two systems using the package size of one pressure switch.
Sigma-Netics
www.sigmanetics.com
Filed Under: Mobile Hydraulic Tips
